The development framework.
WHAT IT IS
A development platform for building applications, with a runtime, libraries and tooling.
WHAT LANGUAGES IT SUPPORTS
C# principally, plus others.
WHAT CHANGED SIGNIFICANTLY
The platform became cross-platform and open source, running on Linux and macOS as well as Windows.
WHY THAT MATTERS
Applications can be hosted on Linux servers and in containers, which changes the hosting economics entirely.
WHAT THE DISTINCTION IS
The older Windows-only framework, still supported but not receiving new features The modern cross-platform platform, which is where development continues
WHAT TO USE FOR NEW WORK
The modern platform, on a current long-term support version.
WHAT APPLICATION TYPES IT SUPPORTS
Web applications and APIs Background services Console applications Desktop applications Mobile applications Cloud functions
WHAT THE RUNTIME PROVIDES
Automatic memory management Just-in-time compilation A comprehensive standard library
WHAT TO ESTABLISH BEFORE DEPLOYING
What your hosting supports.